A silicon controlled rectifier (SCR) clamp is a device often manufactured on-chip to provide electrostatic discharge (ESD) protection. SCR clamps have a large off-resistance, a very low on-resistance, snapback characteristics, and a relatively high turn-on voltage. Therefore, SCR clamps offer excellent protection against ESD events in applications where a high voltage swing is required. Different applications require different voltage swings to be tolerated on the signal or power line. Hence, a tunable trigger voltage is a key feature that is desired for an SCR clamp.
A conventional ESD protection device 1 including a conventional SCR clamp 10, using two bipolar junction transistors (BJTs) 112, 114, in a positive feedback configuration, is shown in FIG. 1. The turn-on, trigger voltage of this SCR clamp 10, by itself, is not tunable. However, external trigger circuits may be used to tune the trigger voltage. For example, a Diode Trigger SCR (DTSCR) clamp uses diodes to tune the trigger voltage. Alternatively, a Grounded Gate Triggered SCR (GGSCR) clamp uses transistors to tune the trigger voltage. FIG. 1 shows a conventional trigger circuit 20 including a diode and a p-type field-effect transistor (pFET).